Nutanix Acropolis Hypervisor (AHV) Changed Block Tracking (CBT) is an optional mechanism that enhances the backup performance of Nutanix AHV virtual disks. When you enable Nutanix AHV CBT, the system uses REST API to detect the changed meta-data regions of the virtual disks by comparing snapshots. With this comparison, Nutanix AHV CBT provides better backup performance than traditional cyclic redundancy check (CRC) backups because the API query identifies the changed regions for the incremental backups as well as identifying those regions that are spare (zeroed), which can reduce read operations for full backups.
How It Works
Nutanix AHV CBT uses REST API to determine the changed meta-data regions in Nutanix AHV virtual disks by comparing two snapshots (a snapshot of the current virtual disks environment against the snapshot that was obtained during the previous CBT-enabled streaming backup). Only the changed meta-data regions that the API detects are backed up and written to backup media. After the backup completes, the current snapshot will become the previous snapshot for comparison in the next CBT-enabled backup operation. Only one snapshot per VM will be retained for comparison.
Note
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When the Nutanix AHV CBT option is disabled, the retained snapshot on the Nutanix cluster will be deleted.
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When the retention rule for backup copies is set to spool copy, for Nutanix AHV CBT, one snapshot per VM will still be retained for comparison purposes.
For more information, see Enabling Changed Block Tracking for for Nutanix AHV.